(1) Field of the Invention
The present invention relates to a display device, particularly to a gas discharge device in which the luminous efficiency is improved and high contrast is sustained by high efficiency of anti-reflection of ambient light.
(2) Description of the Prior Art
In various kinds of conventional gas discharge display devices, cell sheets are usually employed for providing discharge cells therein as exemplified by FIG. 1(a). In FIG. 1(a), a cell sheet CS sandwiched between a front glass plate FG and a rear glass plate RG is provided with plural spaces which are arranged in a for individually forming discharge cells, inner walls thereof being coated with fluorescent layers Ph, display anodes DA and cathode C being arranged in front and rear thereof respectively. These fluorescent layers are excited by ultraviolet rays emitted from gas discharges generated in those discharge cells, so as to radiate desired visible light.
For the cell sheet in the above structure of the gas discharge display device, mechanically workable ceramics for example Macor have been employed and perforated by etching and the like. Otherwise, black banks B formed by firing multilayer-printed black glass paste as shown in FIG. 1(b) are employed for providing the discharge cells.
Among these conventional formations of discharge cells, the former is too expensive to work cell sheets and difficult to form a large scaled display device, as well as to provide miniaturized discharge cells. On the other hand, in a gas discharge display device formed by the latter, the efficiency of reflection of the light emitted from the fluorescent layer Ph toward the front view side upon the light-absorbing black glass paste is too low and hence the luminous efficiency in the front view direction is deteriorated. The removal of black pigments from the black glass paste has been tried, in an attempt to improve the above efficiency of reflection thereon. However, effective improvement of efficiency could not be obtained.
Meanwhile, in order to increase the display contrast in various kinds of display devices including cathode ray tube display devices, gas discharge display devices and low velocity electron beam fluorescent display devices, typically the brightness of display is increased and the reflectance of displaying surface is lowered.
Conventional measures for lowering the reflectance of displaying surface of the display device are as follows.
(i) An absorption type neutral density (ND) filter is employed. PA0 (ii) Rare earth elements, for instance, Nd.sub.2 O.sub.3, are added to the glass material constituting the displaying surface. PA0 (iii) A suitable pigment is added to the fluorescent material constituting the display element. PA0 (iv) The portions other than the fluorescent layer of the display element are coated with black materials. PA0 (v) Granular pigments are deposited on the front surface of the fluorescent layer, so as to form a filter.
In addition, in the display device as disclosed in Japanese Patent Application Laid-open Publication No. 59-36,280, which was filed by the present applicant, as shown in FIGS. 2(a), (b), the display contrast is increased substantially 4 to 6 times together with the being lowered only about by 20% on account of the application of optical filters formed of substantially transparent inorganic materials, through which color light emitted from plural kinds of colored display elements combined with each other into a colored picture display device are transferred respectively, upon those colored display elements. However, even though the above remarkable increase of the display contrast has been attained, the quality of displayed color picture cannot be satisfied under high ambient illumination with respect to the contrast thereof.
In this connection, FIG. 2(a) is a plan view showing a part of the above disclosed gas discharge display device, meanwhile FIG. 2(b) is a cross-sectional view-thereof along the line X.sub.1 -X.sub.2.